between patterns a vst instrument will get stuck and play
the note into the next pattern and through the song.
how do I prevent this from happening?
Patterns combine to form a continuous sequence; they’re not isolated units placed on a single page, as it were, so there’s no implicit noteoff at the end of each one.
All you need to do is put a noteoff command at the start of the next pattern. The note should release as normal according to your VSTi patch’s ADSR envelope. My noteoff is mapped to ‘Tab’, but I can’t remember if that’s universal…check the docs 
As syphus has already mentioned, to stop a sustaining note you can insert a note-off command somewhere after the note itself, positioned within the same note column.
For example:
More info:
http://tutorials.renoise.com/wiki/Note-Off
I personally prefer to put them on the last row of the current pattern, rather than the first row of the next pattern. Feels a bit more logical to me that way, since I can think of that pattern as “safe” and just forget about it. That way I don’t have to remember to add note-offs to any new patterns that I might add later, which I always bloody forget until I’ve rendered the song to .WAV and find myself listening to a horrible cacophony of jumbled notes 
The default mapping is Caps-Lock.
oh! those little offs are note offs?
i see those all over the place but I never manually put them in before.
weird I’ll try it tonight.
thanx guys
Depending on your preferences, they can be inserted into the pattern automatically while you record notes live from your keyboard.
You can also use the matrix for this purpose! Just mute the parts of the song that should be silent.
Notice that matrix-mutes will work instantly when jumping between patterns!
how do I “enter the matrix” lol
feel free to use the matrix portal located in the top right corner of this image:
if you need an exit 
just click it again 
no more messing about with phones… renoise truly is the 21st century level shit! 
If you look carefully, your question already contains the answer…